Apparatus for casting rings

ABSTRACT

The disclosure concerns the casting of pieces, such as rings or the like, having bores extending therethrough from metals subject to substantial shrinkage during conversion from a molten to a solid state. The apparatus employed includes a main mold member having a cavity defined by a peripheral wall and a core member adapted to be moved between a position within the cavity and an elevated position remote therefrom. The core when in the cavity is spaced from the peripheral wall to define an annular molding cavity therewith. The core is cooled as by the circulation of a fluid medium such as cold water therethrough. In the casting of pieces with the mold member and core molten metal is poured into the molding cavity between the core and mold member, the core being in its lowered or active position at this time. The core is retained in such active position only until the metal surrounding the core has solidified sufficiently to be self-sustaining and the core is then immediately elevated to its remote position whereby solidification of the main body of metal and the resultant shrinkage thereof takes place in the absence of the core.

United States Patent 03,570,581

[72] Inventor Richard J. Gennone Primary Examiner-J. Spencer Overholser Wyomissing, Pa. Assistant Examiner-John S. Brown [211 App]. No. 722,801 Attorneys-John R. Bronough, Floyd 8. Levison and E. Dennis [22] Filed Apr. 19, 1968 O'Connor [45] Patented Mar. 16, 1971 [73] Assignee North American Rockwell Corporation Pittsburgh, Pa. ABSTRACT: The disclosure concerns the casting of pieces, such as rings or the like, having bores extending therethrough from metals subject to substantial shrinkage during conversion from a molten to a solid state. The apparatus employed in- 54 APPARATUS FOR cludes 3 main mold member having a cavity defined by a lChimADnwing Figs peripheral walland a core member adapted to be moved between a position within the cavlty and an elevated position U.S. remote therefrom The core when in the cavity is spaced from f 322d 15/02 the peripheral wall to define an annular molding cavity .L therewith The core is cooled as the circulation of a 132,9, 120, 320, 348, 368, 345, 346, 369, 351, medium such as cold water therethrough. 1n the casting of 356, 355 pieces with the mold member and core molten metal is poured [56] References cued into the molding cavity between the core and mold member, the core being in its lowered or active position at this time. UNTED STATES PATENTS The core is retained in such active position only until the 1,387,291 8/1921 Morse 164/345X metal surrounding the core has solidified sufficiently to be 1,683,475 9/1928 Littell 164/345X self-sustaining and the core is then immediately elevated to its 1,387,291 8/1921 Morse 164/132 remote position whereby solidification of the main body of 2,792,605 5/1957 Smith 164/132X metal and the resultant shrinkage thereof takes place in the 3,016,587 l/1962 Brick 164/132X absenceofthecore.

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. A /9 I QMQZA /a 40 Patented March 16, 1971 3,570,581

. l APPARATUS FOR CASTING RINGS BACKGROUND OF THE INVENTION In the casting of various metals which are subject to substantial shrinkage upon solidification such as brass, zinc, ferrous metals and the like to form rings and other shapes involving a central bore the shrinkage of the metal upon solidification results in the contraction of the transverse or diametrical dimension of the bore. Where sand cores are employed as has been conventional in such casting operations no difficulties are encountered as the sand cores do not have the stability to prevent such shrinkage of the metal the core crumbling to the extent necessary to permit the shrinkage to take place. However where permanent casting molds or dies are employed involving a metal core member the contraction of the bore due to the shrinkage of the metal is prevented by the core with the result that through cracks are formed in the cast pieces rendering them unusable.

In an attempt to overcome the aforementioned problem it has heretofore been proposed to heat the core of a permanent mold assembly to a temperature somewhat below the melting temperature of the metal being cast, maintain the core within the main mold cavity until solidification of the metal surrounding the core occurs and then remove the core. The heating of the core was presumed necessary to promote the flow of metal in streams on opposite sides of the core during the pouring operation and the joining of the streams into a homogeneous mass at their juncture point. It has been found in practice however that the heating of the core serves no useful purpose and in fact is deleterious. Thus due to the expansion of the core resulting from the heat applied thereto, the core cannot normally be removed from the cast piece at the time desired and the cracking of the cast piece persists.

SUMMARY OF THE INVENTION As distinguished from the prior proposal described above in accordance with the instant invention the core of a permanent mold assembly is cooled as by the circulation of a cooling medium, such as water, therethrough at the time the metal is poured and during initial solidification thereof around the core. Following the pouring operation and immediately upon the solidification of the metal surrounding the core, which occurs rapidly due to the relatively low temperature of the core, the core is removed to permit the major shrinkage of the cast piece to take place without interference by the core. Such shrinkage cracks which may have been formed in the relatively thin solidified layer surrounding the core before removal of the latter do not prove harmful as at the worst they constitute only surface blemishes on he on the cast piece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a typical cast piece produced by the method and apparatus of the instant invention;

FIG. 2 is a plan view of a permanent mold assembly in accordance with the instant invention;

FIG. 3 is a view taken on the line 3-3 of FIG. 2 looking in the direction indicated by the arrows and with parts in section and other parts in elevation; and

FIG. 4 is a view similar to FIG. 3 illustrating the assembly with a core member thereof elevated to an inactive position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and first to FIG. 1 cast pieces of the type adapted to be produced by the practice of the instant invention are exemplified by the ring having a bore 11. However it will be understood the cast piece may as well be of square, hexagonal, or other configuration with a bore therethrough of the same or different configuration.

For the casting of the piece of FIG. 1, or of a piece of any other configuration having a through bore, a mold assembly as disclosed in FIGS. 2 to 4 is employed the assembly comprising a lower mold or die member 12 and a core member 16. Mold medium such as water through a chamber 19 in the body of the mold. The cooling medium is supplied from any suitable source through a hose or pipe 20 having a fitting 22 secured in a port 23 at one side of mold member 12, the port being in communication with chamber 19. The cooling medium is exhausted from the moldmember through a second hose or pipe 24 similarly connected by a fitting 26 in a port 27 in communication with chamber 19 and located preferably at the opposite side of the mold member from aperture 23.

Mold member 12 is provided with a main cavity 28 having a boundary wall 30 defining the shape of the exterior wall of the piece to be cast therein. The mold member is also provided with a pouring basin, 32 and a runner 34 leading from the basin to the mold cavity.

Core member 16, also suitably made of copper, is supported for vertical movement between the working position illustrated in FIG. 3 in which it is resting on the bottom of the mold cavity 28 and a remote or upper position illustrated in FIG. 4. The means for so supporting the core comprises an arm 36 secured to the core as by stud 37 the arm terminating in a sleeve 38 mounted for vertical sliding movement on a post 40 which is in turn supported'from base 18, the bore of the sleeve and the post suitably being of such cross-sectional shapes as to prevent rotation of the sleeve on the post. The raising and lowering movements of arm 36 and hence of the core may be accomplished in any desired way as for example by an hydraulic piston-cylinder motive unit 42 mounted in fixed position on a bracket 44 secured to post 40, the lower end of the piston rod 46 of unit 42 being threadably connected to arm 36 and locked thereto by lock nut 48. The controls for unit 42 have not been shown and as will be understood may be of any conventional type whereby the unit can be activated at the desired times.

Core member 16 is preferably tapered as illustrated in FIGS. 3 and 4 to promote its removal from a cast piece. Also the core member is provided with an annular channel 50 to receive a circulating cooling medium such as water. In the construction illustrated channel 50 is in the form of an annular recess in the core member proper and is closed, except for fluid entry and exit ports, 53 and 54 respectively, by a circular enlargement 52 of arm 36 overlying the core. The cooling medium, such as water, is supplied from any suitable source through a hose 55 the end of which is provided with a fitting 56 secured in port 53 and is exhausted through a second hose 58 provided with a fitting 60 secured in port 54. To insure precise positioning of the core member 16 in the mold cavity the bottom of the mold cavity is preferably provided with a tapered recess 62 receiving a correspondingly tapered projection 64 of the core member when the latter is lowered to its working position.

In the performance of the method of the instant invention with the apparatus described above, following lowering of the core member to the position illustrated in FIG. 3, molten metal is poured, as by hand, from a suitable ladle, into pouring basin 32 the metal flowing therefrom through runner 34 into the annular casting cavity defined by wall 30 and core member 16, the pouring continuing until the cavity has been filled to the desired height. The core member is then maintained in the position of FIG. 3 for a period sufficient only to permit solidification of the metal immediately adjacent the core to the point that a self-sustaining cast wall surrounds the core, such solidification being rapidly accomplished due to the water cooling of the core. Motive unit 42 is then activated to elevate arm 36 and the core carried thereby to a remote position as illustrated in FIG. 4 the main body of the metal of the casting thereafter being permitted to continue solidification with resultant shrinkage without interference by the core. Following solidification and cooling to the point desired the casting may then be removed from the mold and the operations repeated.

As will be understood, for any particular casting operation the exact timing for the removal of the core from the mold cavity will depend on a number of factors such as the temperature of the molten metal, the dimensions of the piece being cast, the temperature of the cooling medium, etc. Hence such timing is most suitably determined by trial and error. However for purposes of example it will be assumed that the ring to be cast is of the configuration illustrated in FIG. 1, is composed of 60-40 brass (60 percent copper 40 percent zinc) and has a one-eight inch wall thickness and an outside diameter of two and three-quarters inches. Under such circumstances and with the casting metal at a temperature of l,800 F. and the cooling water at a temperature of 60 F. it has been determined that the core should remain within the cavity for approximately two-tenths of a second after the completion of the flow of metal therearound.

Having thus described the invention in rather complete detail it will be understood that these details need not be strictly adhered to, and that various changes and modifications may be made all falling within the scope of the invention as defined by the following claims.

l claim:

1. In a method of casting a piece having a through bore from a metal subject to shrinkage upon solidification the steps comprising defining a mold cavity whose outer wall is defined by a metal mold member and whose inner wall is defined by a core adapted to be shifted between a position in which it forms the inner wall of said cavity and a position remote therefrom, positioning said core to form said inner wall, pouring said metal in a molten state into said cavity while simultaneously liquid cooling both said metal mold member and said core, said core being cooled by introducing said liquid through the top of said core into an annular recess withinsaid core, circulating said liquid to an exhaust outlet located at the top of said annular recess, and exhausting said liquid through said exhaust outlet, permitting said core to remain in its inner wall forming position for a period sufi'lcient only for the metal adjacent said core to solidify to a self-sustaining condition and then moving said core to said remote position and retaining it therein until the piece is removed from said mold cavity. 

1. In a method of casting a piece having a through bore from a metal subject to shrinkage upon solidification the steps comprising defining a mold cavity whose outer wall is defined by a metal mold member and whose inner wall is defined by a core adapted to be shifted between a position in which it forms the inner wall of said cavity and a position remote therefrom, positioning said core to form said inner wall, pouring said metal in a molten state into said cavity while simultaneously liquid cooling both said metal mold member and said core, said core being cooled by introducing said liquid through the top of said core into an annular recess within said core, circulating said liquid to an exhaust outlet located at the top of said annular recess, and exhaustiNg said liquid through said exhaust outlet, permitting said core to remain in its inner wall forming position for a period sufficient only for the metal adjacent said core to solidify to a self-sustaining condition and then moving said core to said remote position and retaining it therein until the piece is removed from said mold cavity. 